The present invention relates to overhead cranes which are used to support critical loads such as extremely expensive generator-turbine components used in a powerhouse, or hazardous materials such as molten metal.
Overhead cranes of the type referred to generally comprise a trolley supported on overhead tracks or rails. The trolley in turn supports a large power driven cylindrical drum. A wire rope is wound around the drum and used to support a load bearing hook and to lift a load suspended by the hook. Since even the utmost care in manufacturing cannot completely preclude the possibility of failure of any single component of the crane, it is desirable when handling critical loads to provide an auxiliary or redundant means for supporting the load in the event of a failure of one of the crane components. The prior art means of compensating for such failure has generally comprised the use of two hoist drums for supporting the load. Other more recently developed means include the use of hoist drum catchers positioned beneath the hoist drum and functioning to support the hoist drum in the event of the failure of its other support means. See, for example, U.S. Patent application Ser. No. 653,741, filed Jan. 30, 1976 by Raugulis et al. and assigned to an assignee in common with that of the present invention. Providing a catcher positioned below the hoist drum is effective to prevent the load from being dropped, however, such a redundant drum support means is limited in that it requires that the load either be held in suspension or set down upon failure of a drum support component and does not permit raising of a load for proper disposal of the load.